Best Practices for Operating with Diesel Exhaust Fluid (DEF) in Cold Weather

Did you know that Diesel Exhaust Fluid (DEF) can freeze?
DEF will freeze at 12° F when not in use and will ‘slush’ before then. DEF is typically 32% urea and 68% deionized water. At this ratio both ingredients will freeze and thaw at the same speed. The process of freezing and thawing has no effect on the performance of the DEF.

Make room for expanding fluid
Just like water, DEF expands when it freezes – with about 7% growth in volume. Don’t fill your DEF tank completely in cold weather. If the fluid freezes and expands, the container may crack.

Don’t trap DEF in hoses
After you shut down your equipment, wait 60 seconds before turning off the battery. The delay allows any remaining fluid to drain out of the hoses, back into the tank, lowering the likelihood of damage from DEF freezing.

Allow the DEF to thaw before use
The SCR systems found in equipment are designed with heating elements to thaw frozen DEF with the engine running. If the DEF is frozen, allow the machine to heat and thaw the material before operating to avoid machine damage.

Never use anti-gelling additives
Adding anything to DEF, including a freeze point improver, can cause the SCR system to function incorrectly and, ultimately, damage the SCR system components.

Check gauges and levels to make sure you’re operating with enough DEF
Keep an eye on the DEF gauge the same way you watch your fuel gauge. Equipment with low DEF levels will be limited to lower operating speeds until the fluid is replenished.